Nitrous oxide remains the most commonly used anesthetic and has been given to several billion patients. In vitro, even brief exposure to nitrous oxide inactivates methionine synthetase, which reduces induction of enzymes required for immune function. Nitrous oxide also reduces chemotactic migration by monocytes. However, nitrous oxide improves neutrophil chemotaxis and facilitates oxygen radical formation, and may therefore augment the efficacy of oxidative killing by neutrophils - the primary defense against pathogenic bacteria. Preliminary results in 200 patients suggest that the beneficial effects of nitrous oxide on wound healing outweigh its toxicities. We will thus test the hypothesis that the incidence of postoperative wound infection will be less in patients given 60% nitrous oxide than in those given 60% nitrogen during elective colon surgery. We propose to study up to 1000 patients undergoing elective colon resection. Perioperative antibiotic, anesthetic, fluid, and oxygen management will be set by protocol. Patients will be anesthetized with isoflurane in 40% inspired oxygen, with the remaining ventilatory mixture randomly assigned as nitrous oxide or nitrogen. Surgical wounds will be evaluated daily by a physician blinded to group assignment. Wounds will be considered infected when they meet CDC criteria or pus is detected and they are culture-positive for pathogenic bacteria. As a secondary outcome, incidence of nosocomial pneumonia in the two groups will be determined. Results will be analyzed by Fisher Exact and unpaired, two-tailed t-tests; P < 0.05 will be considered statistically significant. We anticipate showing that substituting nitrous oxide for nitrogen reduces the incidence of surgical wound infection. Confirming our hypothesis would thus allow clinicians to make a minor modification in anesthetic practice that might reduce the incidence of a complication responsible for considerable perioperative morbidity and cost.